1. Field of the Invention;
The present invention relates to an apparatus for deicing of trolley wires. More specifically, the present invention relates to an apparatus for deicing trolley wires in a power transmission system comprising at least two trolley wires for supplying an alternating current power to an electric vehicle.
2. Description of the Prior Art;
Water, snow etc, if any, on trolley wires installed in a power transmission system for supplying an alternating current power to an electric vehicle is frozen to form a ice layer on the trolley wires when the ambient temperature or the temperature of trolley wire becomes lower than the freezing point. The ice layer prevents an electrical contact with a pantograph of an electric vehicle. As a result, a supply of an electric power from the trolley wires to an electric vehicle is disturbed and a pantograph is broken. For this reason, the operation of electric vehicles is often obstructed.
A prior art system for deicing of trolley wires which is of interest to the present invention is disclosed in Japanese Published unexamined utility model application No. 131601/1974, laid open Nov. 12, 1974 for public inspection. FIG. 1 shows a schematic diagram of the prior art system for deicing of trolley wires as disclosed in the above referenced Japanese Utility Model Laying Open Gazette. Referring to FIG. 1, a trolley wire 11 for supplying an electric power to an electric car is suspended from a stringing wire 13 by means of a plurality of electrically insulating hangers 12 and electrically conductive hanger 12'. The plurality of hangers 12 are provided to hang the trolley wire 11 from the stringing wire 13, with the trolley wire 11 electrically insulated from the stringing wire 13, while the hangers 12' are set in the vicinity of the feeding points 14 and 14' so as to electrically connect the corresponding points at the trolley wire 11 to the feeding points 14 and 14'. The feeding points 14 and 14' are connected to a feeder wire cable 15 at predetermined intervals of distance for the purpose of feeding a voltage to the trolley wire 11, thereby to compensate for a voltage drop along the trolley wire 11. As a result, a closed loop is formed by means of a portion of the feeder line 15 and the trolley wire 11, coupled to each other at the feeding points 14 and 14' through the hangers 12'. A rail installed beneath and along the trolley wire 11 forms a return circuit of a current flowing from the trolley wire 11 through a pantograph of an electric car and wheels thereof to the rail 16. A primary winding 171 of a transformer 17 is connected between the feeder line 15 and the rail 16. A secondary winding 172 of the transformer 17 is provided to transform the voltage applied to the primary winding 171 to a lower voltage and is connected to a full wave rectifier 18. The full wave rectifier 18 comprises a bridge circuit of diodes, connected in a well known fashion, and the direct current output is applied to the above described closed loop formed by the feeder line 15 and the trolley wire 11. The direct current output terminals of the full wave rectifier 18 may be shunted with an alternating current bypassing diode 19. With such a circuit configuration, a direct current is caused to flow through the above described closed loop comprising the feeder line 15 and the trolley wire 11 and the said direct current is superposed on the alternating current flowing through the trolley wire 11. As a result, the current flowing through the trolley wire 11 is increased and a Joule heat is produced along the trolley wire 11, thereby to deicing of the trolley wire 11.
However, the above described prior art system requires the transformer 17 and the full wave rectifier 18 for the purpose of applying a direct current to the trolley wire 11 to deicing of the trolley wire, with the result that the circuit configuration becomes complicated and expensive. In such a power transmission system where a single trolley wire and the rails are utilized for supplying an electric power to an electric vehicle, a very high voltage power of such as several thousand volt to several ten thousands volt should be transmitted and this necessitates transformation of the said very high voltage to an appropriate voltage suited for rectification into a direct current voltage to be supplied to the trolley wire for the purpose of deicing of the trolley wire, with the result that the transformer 17 should be extremely large sized and becomes expensive. In addition, in order to apply the output of the full rectifier to the feeder line and the trolley wire, some connections for such direct current circuit need be separately provided, which makes installation complicated and expensive. Furthermore, as the output direct current from the rectifier is divided into two parts at the connection point of feeder line, only one part of the divided current is effective to increase a Joule heat in the trolley wire 11. As a result, deicing of the trolley wires need much electric power, resulting in lower efficiency.
Another example of interest to the present invention for an apparatus for deicing of trolley wires is seen in Japanese Published examined patent application No. 42805/1976, published Nov. 18, 1976 for opposition. More specifically, the referenced Patent Publication Gazette discloses that both a trolley wire for an up line and a trolley wire for a down line of a double track are connected at the terminations to form a closed loop and a separate power source for supplying a power for deicing is provided in a power source for supplying an electric power to both trolley wires, such that an alternating current is applied from the substation to the closed loop formed by the trolley wires of the up and down lines, whereby an additional electric power is applied to the trolley wires and a icing of the trolley wires is prevented or unfreezed. However, the above described deicing apparatus requires a double track including an up and down lines. For this reason, the apparatus disclosed in the referenced Japanese Patent Publication cannot be applied to a single track. In addition, the closed loop formed by the up and down lines becomes so large as to cover a distance between two adjacent substations coupled to the double track. As a result, a deicing operation should be effected in such a large closed loop and a localized deicing operation cannot be effected such that a freeze of the trolley wires is prevented only in a relatively short span of the trolley wires where prevention of a icing is required by virture of meteorological conditions in such a local area. For this reason, the system disclosed in the latter referenced Patent Publication involves a problem of an increased power loss.